The present invention relates to a combined computer and decoder system for receiving broadcast digital transmissions. The invention equally extends to each of the elements of a computer and a decoder adapted for use in such a system.
Broadcast transmission of digital data is well-known in the field of pay TV systems, where scrambled audiovisual information is sent, usually by a satellite or satellite cable link, to a number of subscribers, each subscriber possessing a decoder or receiver/decoder capable of descrambling the transmitted program for subsequent viewing. Terrestrial digital broadcast systems are also known.
More recently, it has been proposed to use such digital broadcast technology for the distribution of other types of digital data and information. Broadcast transmission possesses a number of advantages in comparison with other telecommunication networks, such as the telephone network, notably in relation to increased bandwidth, reliability of transmission etc. For this reason, a number of systems have been suggested using a cable or satellite link to enable access to the internet, for example.
At present, the provision of such services is at a very early stage and conventional hardware and software systems that have been proposed in this regard are often ill-adapted for the applications in question. In the case of a digital television receiver/decoder, for example, the system is usually piloted by means of a television style remote control device. Whilst a remote control of this type is usually sufficient for television applications (channel changing, selection of programme guides or menus), more sophisticated applications such as an internet browser will usually require a keyboard for ease of operation. Similarly, depending on the application in question, the available memory of the decoder may be inadequate for effective operation.
For these reasons, a combination PC/decoder arrangement may be envisaged. However, whilst the theoretical advantages of such a combination may be foreseen, the practical details of the implementation of such a system can give rise to a number of other problems, in particular in respect of the communication of information between the two, how the decoder is configured to handle different types of data, how the decoder changes between different modes of operation (e.g. television/internet modes) etc.
It is an object of the present invention to provide a practically realisable decoder/computer combination that enables digital data to be downloaded from the decoder to the computer whilst avoiding any potential operational problems arising from interaction between the elements of the system.
According to the present invention there is provided a combined computer and decoder system for receiving broadcast digital data transmissions, characterised in that the decoder comprises a routing means, broadcast digital data received at the decoder and destined for the computer being identified and routed to applications within the computer by said routing means.
The presence of a routing means within the decoder enables the decoder to simply and effectively identify messages intended for applications within the decoder and permits the decoder to reject, for example messages having another destination.
In a computer/decoder arrangement, the majority of data received via the decoder during operations in this mode will be routed to the computer for further processing. However, in certain cases, data may be routed to applications within the decoder itself.
For example, the decoder may include an application for surveillance of transmission. In one embodiment, the application may monitor the continuity of the transmitted messages, for example, by checking the arrival of each message in a numbered sequence of messages. In this case, the data representing the message number is passed to the surveillance application.
Alternatively, certain standard test messages may be passed to a stack within the memory of the decoder to permit the decoder to evaluate the quality of the transmission channel based on the received message composition.
Received broadcast data may also be used by decoder based applications to modify the routing table, as will be described below.
In one particularly preferred embodiment, the decoder further includes an application within the decoder adapted to configure operating parameters of the decoder including, inter alia, the routing means. This configuration application and the parameters thereof may be loaded into the decoder or modified by instructions received from the computer. Alternatively, or in addition, the configuration application together with data representing the initial configuration parameters may be stored in the memory of the decoder during the manufacture of the decoder, to permit the auto-configuration of the decoder when the decoder is powered up.
Advantageously, the configuration application may further be loaded into the decoder or modified by instructions received in the transmitted broadcast data. This realisation enables the decoder to be reprogrammed at a distance by instructions contained in the broadcast data flow.
In practice, the routing means may be adapted to identify and route messages according to characteristics of the message data received. In one embodiment, broadcast data received in the MPEG format by the decoder is routed by the routing table according to the value of the packet ID header.
Broadcast digital data routed to the computer may simply comprise data to be processed by applications previously installed in the computer, e.g. applications stored on a diskette and loaded into the computer. However, in one embodiment, the broadcast data may also comprise the applications themselves, adapted to be routed to the computer for execution within the computer. In this way, downloading at a distance of applications into the computer from a remote server may be carried out.
In the case where the transmitted data is non-confidential and/or provided by a free service provider (as may be the case for certain internet applications) the data may be transmitted in clear over the air. However, in the case where the transmitted data sent to the computer is proprietary or otherwise valuable, means for restricting access to the data is desirable.
Preferably, the decoder further includes decryption means adapted to decrypt digital data broadcast in a scrambled form for subsequent routing in decrypted form to the computer. In one realisation, scrambled data is transmitted together with a control word for descrambling of the data, the control word itself being encrypted by a so-called exploitation key and transmitted in encrypted form. The decoder possesses an equivalent of the exploitation key to decrypt the control word and descramble the data. These and other such security measures known from the decoding of television data may be advantageously used in the present system to restrict access to data intended for applications within the computer.
In the above embodiments, operation of the routing means has been discussed mainly in relation to data received via the broadcast transmission link destined for the computer or decoder. However, as will be appreciated, the routing means may also operate to route digital data received from other sources, such as applications within the decoder and/or within the computer and data received via any of the other input ports of the decoder, such as a serial/parallel link etc.
In the case where the computer/decoder combination is to be used in an interactive application, such as an internet application, the computer may be linked to a modem such that messages may be sent from the computer to a server at the broadcast centre or elsewhere to demand, for example, the transmission of a defined home page or the like. However, this may increase the cost of the system to the user.
Preferably, the decoder further comprises a modem, the routing means being adapted to route selected messages received from an application within the computer to the modem. In practice, nearly all receiver/decoders intended for the digital television market possess a modem link and the cost of the modem is absorbed in the cost of the decoder itself.
As mentioned in the preamble of this application, problems of communication and conflicting commands may arise with a decoder and computer combination. In a particularly preferred embodiment of the invention it is foreseen that the operation of the decoder is at least in part controlled by control signals sent from a control means within the computer.
By transferring control of the decoder to the computer, the operation of the system can be more easily managed. For example, in one embodiment, the computer controls the operation of the tuner within the decoder to select the channel frequency for reception of digital data to be downloaded to the computer. Since this information may be known to the application within the computer, but not to the decoder, automatic selection of channel frequency by the application considerably simplifies the setting up of the system for an operator.
Potential conflicts between instructions sent to the decoder by other means, such as the decoder remote control, and instructions originating from the computer can also be avoided by such a transfer of control.
For example, the computer may be adapted to send a control signal to the decoder to render the decoder unresponsive to selected commands received from selected other decoder inputs, such as a change channel command from the decoder remote control. In some embodiments the decoder may still be enabled to receive commands from other input sources, for example commands received in the broadcast data flow.
As will be understood, the computer/decoder set-up of the present invention may be used in a number of commercial applications, ranging from mass market internet type browser applications to more specialised applications intended for corporate organisations, where the broadcast link is used to send proprietary data.
One example envisaged is for the transmission of financial information, notably stock price information, from a central financial centre to a number of remote terminals. In such an application, the customer benefits from the increased channel capacity as compared to standard telecom networks together with secure protection of sensitive data by means of an encrypted transmission (where provided). In this embodiment, the decoder will serve exclusively as a channel for information destined for the computer and will not handle television transmissions.
In contrast, where the decoder is to be used in the context of a mass market product, it is obviously advantageous that the decoder may also be used in its normal configuration, i.e. to receive and process digital television signals. In this case, the system further comprises a television display, the decoder being adapted to process received broadcast audio-visual data subsequently sent to the television display.
The present invention further extends to a computer and decoder for use in a system as described above.
Whilst the application refers to  less than  less than receiver/decoders greater than  greater than  and  less than  less than decoders greater than  greater than  it will be understood that the present invention applies equally to embodiments having a receiver integrated with the decoder as to a decoder unit functioning in combination with a physically separate receiver. Such a decoder may be of the kind used in any satellite, terrestrial, cable etc digital broadcast system and may include other multimedia type capabilities.
There will now be described, by way of example only, an embodiment of the present invention, in which: